The green fluorescent protein (GFP) from the jellyfish Aequorea victoria has been extensively used as a marker of gene expression and protein targeting in intact cells and organisms. Since GFP has no toxic effect on cells and it is easy to detect, it can replace controversial transformation markers such as those for antibiotic or herbicide resistance. The protein can also be used to detect dynamic responses of signal transduction pathways, subcellular localisation of chimeric proteins, and transfection efficiency. It allows visualisation of the organelles and observation of many important cellular processes.